Apple scab, caused by the fungus Venturia inaequalis, is a major problem for growers of apple trees. Apple scab causes dark lesions on the leaves, bark, buds and fruit of the trees. The disease causes significant crop yield losses each year because the infected fruit is not marketable. The disease also causes damage to ornamental apple trees.
There are generally two phases to apple scab infection. When the temperatures begin to warm up, Venturia inaequalis spores are blown onto the bark and leaves of the apple trees. Later in the season, secondary infections begin as the fungi release more spores which infect new fruit and additional leaves.
Currently, it is very difficult to control apple scab for several reasons. First, Venturia inaequalis has developed resistance to some fungicides, such as benzimidazole and strobilurin/quinone fungicides. Secondly, some effective fungicides, such as benzimidazole fungicides, are being banned in some areas because they are harmful to the environment or humans.
Yet another issue is that often the currently available treatments have to be re-applied repeatedly to be effective and in order to treat secondary infections. Some apple orchards are treated with fungicides for apple scab up to 12 times in a growing season. The extra applications add to the expense of disease control because more of the product must be purchased, and significant time and labor resources are used during the subsequent applications. Further, each new application increases the risk of exposure of the product to non-target trees.
Another problem is that some treatments require that the leaves and fruit be treated. For example, some contact fungicides, such as Captan (N-trichtoromethylthiocyclohexene-1,2-dicarboximide, available from Southern Agricultural Insecticides, Inc.), are effective against apple scab. However, Captan has no systemic control activity so it must be applied directly and repeatedly to the infected areas. A lot of product must be used and the techniques are often dangerous and/or wasteful. For example, if a tree's leaves are infected, comprehensive treatment requires application of the product to the leaf surface. Given the size of trees, it is difficult to apply the product to the leaves. One application method requires the user to tediously spray the leaves with a low pressure sprayer in close proximity to each leaf. For a home owner or backyard gardener, this method may require the user to use a ladder or other tool to elevate himself to the leaves. The user must be careful not to damage the tree by climbing or other similar means of accessing the leaves. Alternatively, a high pressure sprayer could be used. For this application method, the user could be on the ground, however, this method results in drift of the product to the surrounding area. The drift can require that people, animals, and non-target tree species be removed from the area of treatment or otherwise protected from the product by sufficient physical barriers. These additional measures required for safe and effective foliar spray applications are costly and inconvenient.
In the past, bark spray applications have been used with limited success. The treatments resulted in ineffective or unpredictable disease control in trees because the fungicides were not able to penetrate the tree bark and/or the tree could not transfer them to the areas in need of treatment.
Other means of treating trees are available but have proven to be ineffective or impractical to implement. Some methods require professionals who are trained in specialized equipment to apply the product. Other expensive methods include invasive drilling, bark injections, or high-pressure root flare injections. For example, there has been a fungicide that provided some systemic fungal protection, however, it was effective only when injected directly into the tree.
3-(Difluoromethyl)-1-methyl-N-[(3R)-1,1,3-trimethyl-2,3-dihydroinden-4-yl]pyrazole 4 carboxamide has the following structure:

U.S. Pat. No. 8,580,836 discloses that carboxamide compounds can be sprayed to the bark of trees to control diseases. This patent, however, fails to disclose or suggest the use of 3-(difluoromethyl)-1-methyl-N-[(3R)-1,1,3-trimethyl-2,3-dihydroinden-4-yl]pyrazole-4-carboxamide to treat apple scab by bark spray treatment.
Therefore, there is a need in the art for safe and effective methods for providing long-term and systemic protection to apple trees from apple scab infection.